A non-volatile memory, such as Flash memory, retains stored data even if power to the memory is removed. A non-volatile memory cell stores data for example, by storing electrical charge in an electrically isolated floating gate or in a charge-trapping layer underlying a control gate of a field-effect transistor (FET). The stored electrical charge controls the threshold of the FET, thereby controlling the memory state of the cell.
It is common to monolithically incorporate multiple types of field-effect devices on the same substrate as memory cells. Those non-memory devices perform for example, decoding, charge-pumping, and other functions related to memory operations. The substrate may also include non-memory devices to provide functions that are not related to memory operations. Such non-memory devices incorporated on the same substrate as the memory cells may include transistors tailored for high-speed operations, while other transistors are tailored for handling high operating voltages. Integrating the processing of memory cells, such as a split-gate memory cell, with the processing of one or more types of non-memory transistors on the same substrate is challenging as each requires different fabrication parameters.
Additional types of integrated circuits, such as analog devices pose manufacturing challenges. Many analog devices, such as a low noise amplifier, have more stringent noise tolerances than FET devices used in digital logic. Mixed signal electronics, those with integrated digital and analog signals, can be found in music players, cameras and cellular telephones. As with the memory cells, these analog devices pose fabrication challenges due to the different lubrication parameters. Accordingly, there is a need for device and methods for integrating field effect transistors and other devices on the same substrate to facilitate improved cost, performance, reliability, or manufacturability.